Effect of BaTiO3 as a filling material with adjustable dielectric properties on improving the radio frequency heating uniformity in red jujubes

The non-uniformity of radio frequency (RF) heating is a major obstacle to develop successful large-scale disinfestation processes for agricultural products with large particles. To effectively improve the RF heating uniformity in red jujubes, the chemical material of BaTiO3 (BT) with different volume percentages was added into food-grade silicone (FGS) to form FGS/BT composite particles with various dielectric properties. The various FGS/BT composite particles were filled inside the rectangular container of red jujubes and used to evaluate the effect of matching degree of their dielectric constants on the RF heating uniformity. The results showed that the dielectric constant of the composite increased from 3.41 ± 0.14 to 8.31 ± 0.15 as the BT volume percentage increased from 0% to 20% at 25 °C and 27.12 MHz. Compared with FGS, the filled FGS/BT composite with a BT volume percentage of 20% not only improved the heat conduction but also optimized the temperature distributions among red jujube particles, which reduced the heating uniformity index in the top, middle, and bottom layers by 40%, 32%, and 27%, respectively. As the electrode gap increased from 160 mm to 180 mm, the heating rate and uniformity index in FGS/BT filled samples decreased significantly (p < 0.05). There was no significant (p > 0.05) difference in color and textural properties between the treated and control samples. This study provided the effective filling materials with matched dielectric constant in the RF treatment of red jujubes and a feasible method to further improve the RF heating uniformity in large-size agricultural products.